Deaerators are widely used in the petrochemical, refining, and power generation industries. A deaerator is a mechanical piece of equipment that is used to heat boiler feed water and to remove oxygen and carbon dioxide from boiler feed water, prior to the water being fed to the boiler. Oxygen and carbon dioxide contained within boiler feed water cause significant corrosion in the steam system, namely the boiler tubes, steam lines, condensate lines, and heat transfer equipment. Additionally, if the boiler feed water has oxygen in it, the oxygen may cause corrosion to surface condensers which may release copper. The released copper in the steam system may create a major problem when it is necessary to make any repair welds to the steam system. Use of a deaerator substantially decreases the amount of corrosion that develops in the steam system by the removal of oxygen and carbon dioxide.
Deaerators use a mechanical stripping mechanism to release the oxygen and carbon dioxide contained within the boiler feed water. Several types of stripping mechanisms are commercially available for deaerators. In large plants that have high steam capacity requirements, a tray deaerator is typically used. In smaller plants that have a lower steam requirement, a packed column or spray type deaerator is used. Although deaerators are able to remove a large portion of the oxygen and carbon dioxide, many times the stripping capabilities of the deaerator are inadequate to remove enough oxygen and carbon dioxide to sufficiently minimize corrosion within the steam system.
Because deaerators are only able to remove a portion of the oxygen from boiler feed water, many petrochemical facilities use chemicals that are commonly referred to as “oxygen scavengers” to further reduce the amount of oxygen in the boiler feed water. Example oxygen scavengers include sulphite, tannin, and caustic based chemicals. Oxygen scavengers are very expensive and add considerable operating costs to the steam system.
Although chemicals, such as oxygen scavengers, are available to remove oxygen from boiler feed water, most plants still have the need for a deaerator. The deaerator has additional advantages to using it, in addition to reducing components that cause corrosion in the steam system. The deaerator can also provide an effective means for recovery of heat from the boiler exhaust or flash steam. The deaerator can also recover condensate from the steam system to reduce amount of make up water that is required to be fed to the boiler.
A need exists for an economical process that is capable of removing oxygen from boiler feed water to supplement or replace the use of a deaerator. It would be advantageous for the process to also remove other gases, such as carbon dioxide, that also cause corrosion within the steam system. It would also be advantageous if the process could be used with new deaerator systems and existing ones, and in particular existing, operating systems.